There are numerous syringes available for drawing a patient's blood. Many syringes have a movable plunger for assisting in the drawing of blood and/or exiting blood from such a syringe. However, there are also syringes that are plunger-less syringes that collect blood by relying on the pressure of the blood within a vein or artery to fill a receptacle such as a capillary tube such as U.S. Pat. No. 4,393,882 filed Nov. 17, 1980. Accordingly, some such plunger-less syringes have an opening to the interior of the blood collecting receptacle that is opposite to where the blood enters the receptacle so that air within the receptacle exits as the blood enters. This has the advantage of allowing the air to escape so that there is no air pressure build up in the receptacle that could inhibit the flow of blood into the receptacle. However, air may remain in contact with the drawn blood which can compromise blood analysis assays, such as the determination of O2 in the blood collected blood.
It is also known and if all the air can be expelled from the receptacle, then a more accurate blood analysis can be performed regarding such gases as O2 that otherwise might diffuse out of the collected blood.
In order to reduce or eliminate air contact with the collected blood, various techniques are known for closing air exit openings in the blood collection receptacles of plunger-less syringes. In one technique, a filter is provided in the air exit opening such that the filter allows air to escape until blood commences to saturate the filter, but after the filter is saturated, it blocks both blood and air from entering and exiting the blood collection receptacle via the opening. In a second technique disclosed in U.S. Pat. No. 4,133,304 (i.e., the '304 patent), an elastomeric seal is provided in the air exit opening, wherein the seal includes a sealable orifice having a retaining element therein (e.g., a thread of a fibrous material). Air and/or blood are able to exit, via the orifice, out of the blood collection receptacle (denoted a “capillary tube” in the '304 patent) until the retaining element is removed from the orifice causing the orifice to close and thereby preventing further contact between the collected blood and the air external to the receptacle. However, the syringes of the '304 patent require assembly wherein, e.g., the capillary tube is fitted within an exterior housing. Moreover, the fitting is only a frictional fitting provided at the needle attaching end of the housing; thus, the receptacle and housing are not designed to remain attached to one another during extensive handling and/or storage. But separation and removal of the capillary tube from the housing has drawbacks in that for the plunger-less embodiment disclosed: (a) during separation, the opening for receiving the drawn blood is apparently unsealed, and presumably remains unsealed until an extra step of resealing is performed, and (b) since the quantity of blood drawn may be small (particularly from infants), such capillary tubes are typically, as their name implies, thin and accordingly not conducive to direct user handling.
Thus, it would be desirable to have a plunger-less syringe wherein: (a) substantially all the air in the blood collection receptacle is expelled as blood is being collected, (b) there is a reduced amount of assembly and/or disassembly immediately prior to and/or after use, and (c) the syringe has an exterior housing that is sized for ease of user handling while the blood collection receptacle therein is sized to accept only the volume of blood needed, and wherein the exterior housing and the receptacle are suitably secured together so that the entire syringe can be handled and/or stored with collected blood therein.
Additionally, note that although plunger-less syringes can be less expensive to produce than syringes with plungers, and can be substantially smaller, plunger-less syringes typically have no means for controlling the movement of blood into or out of their blood collection receptacles. Thus, e.g., in cases where arterial blood is being drawn and there is insufficient blood pressure to draw the blood, alternative blood drawing syringes may be used, or specially designed additional components may be required (as is disclosed in the '304 patent discussed above). Accordingly, it would be also desirable to have plunger-less syringe, wherein a conventional plunger type syringe could be attached thereto for assisting in the withdrawing of a patient's blood.